Which is correct? Your Garmin or the RD? (Read 325 times)

I was just reading another thread somewhere else and it had several comments by people that run races on certified courses while wearing garmins. If they finish the race and their personal garmin does not state they ran the race distance they will go out and run more until their garmin says they ran the correct distance.

My question is, which is correct? The certified course or your garmin?

Second question, you run the same 10 mile race with 3 friends and you all wear a garmin. At the end of the 10 mile certified course you have 9.8 miles, friend 1 has 9.6, friend 2 has 10.2 and friend 3 has 10.4. Who is correct? Do you and friend 1 have to go run further to make up the difference?

If a course is short or long, that's another story. I almost always assume Garmin error, but I am talking about the outlying situations like, "Oh, yeah, one of the volunteers put the finish chute in the wrong place."

On trail races, especially, I consider my Garmin to be at best approximate.

"When a person trains once, nothing happens. When a person forces himself to do a thing a hundred or a thousand times, then he certainly has developed in more ways than physical. Is it raining? That doesn't matter. Am I tired? That doesn't matter, either. Then willpower will be no problem." Emil Zatopek

It's somewhere in the middle. The certified course is measured assuming the tightest corners which runners are not often following as exactly. I run the course and if it's a bit off, I don't stress it. I don't go run extra.

"Don't feel like running today...suck it up and run ...you're an athlete." (John Stanton, founder & owner of The Running Room)

As has been said a certified course is measured at the shortest distance or tangent points on curves - something most runners are actually able to run. This can be demonstrated by thinking about concentric circles, the circumference of the inside circle, e.g. certified distance is less than the circumference of the outside circle. By how much depends on how much larger the diameter of the outside circle is and how long someone runs along that line. In long races on wide curvy streets/trails this can be significantly longer than shortest certified distance.

Garmin's are mechanical/electronic devices with built in tolerances otherwise known as "errors" and most often will show a run longer than race distance - if it hasn't lost lock during the run. Running amongst tall buildings, or under cover of dense tree cover can cause Garmin's to lose lock and who knows what they are measuring at that point.

bob e v 2014 goals: keep on running! Is there anything more than that?

Complete the last 3 races in the Austin Distance Challenge, Rogue 30k, 3M Half, Austin Full

I was just reading another thread somewhere else and it had several comments by people that run races on certified courses while wearing garmins. If they finish the race and their personal garmin does not state they ran the race distance they will go out and run more until their garmin says they ran the correct distance.

Well geez, I thought I would leave that FB thread from hell and come here, for a breath of fresh air...

Who is correct? Do you and friend 1 have to go run further to make up the difference?

Though I suspect you ask the questions tongue-in-cheek as you have a reputation for organizing very well-run events....

Neither. As your example illustrates, it is easy to demonstrate to people that GPS is not infallibly accurate by having a group run together and then show that there are differences between their GPS units that cannot be explained away since they ran together.

The certified course is not accurate either, by design. An accurately certified course will always be a bit long.

"If you want to be a bad a$s, then do what a bad a$s does. There's your pep talk for today. Go Run." -- Slo_Hand

MTA fixed the links. Also would not mind if Garmin measures a bit long, but if its short, assume a missed turn or wrong course ran.

MJ5

Chief Unicorn Officer

posted: 5/14/2013 at 1:07 PM

If my Garmin is within .05 or so for a shorter race like a 5K (say, 3.07), I accept the course as accurate. Especially courses with lots of turns, or pinpoint turns, sometimes the Garmin is thrown off. Plus my understanding of GPS technology is that it plots points as it is measuring and just connects those points with straight lines to measure the distance. That makes me a little skeptical of exact Garmin measurements.

If my Garmin is within .05 or so for a shorter race like a 5K (say, 3.07), I accept the course as accurate.

I ran a 3.18-by-Garmin 5K last weekend; missed my PR by 4 seconds. I'm sure the course is correct; I was just bummed because I kept my Garmin average pace 7 seconds under what I needed; typically 3-5 is safe for Garmin error. Oh well.

Plus my understanding of GPS technology is that it plots points as it is measuring and just connects those points with straight lines to measure the distance. That makes me a little skeptical of exact Garmin measurements.

That's one issue. Another is that the individual points are noisy; they can be 20-30 feet off, under *good* conditions. That said, the unit does do some smoothing to try to correct for both of these. But it's still based on underlying noisy, sparse data.